The rapid growth in the number of Internet users and of services provided through the Internet has been one of the most remarkable phenomena in communications in recent years. Another current trend is the rapidly increasing use of various mobile terminals, such as laptops, PDA (Personal Digital Assistant) equipment, and intelligent telephones.
These two rapidly evolving network technologies, wireless communication and the Internet, are gradually converging to make the packet-switched data services used in the Internet available to mobile users. So far this converging development has occurred rather slowly, since most of the technology developed for the Internet has been designed for desktop computers and medium or high bandwidth data connections. It has therefore been difficult to introduce the IP-based (IP; Internet Protocol) packet services to the mobile environment, which is characterized by less bandwidth and poorer connection stability, as compared to fixed networks, and where the terminals have many fundamental limitations, such as smaller displays, less memory, and less powerful CPUs, as compared to fixed terminals. However, this development will occur at an increasing rate in the foreseeable future. This means that the services first introduced for fixed terminals will gradually be available also for mobile terminals.
One of the first multimedia services introduced for fixed terminals has been the so-called Video-on-Demand service, whereby viewers can use their telephone line to access a video server located in the network. Due to a reverse control channel from an individual user to the server, the service can be used in the same way as a conventional video cassette player, i.e. the film can be played backwards or forwards, stopped, or played in slow motion.
In these systems the users utilize the services independently of each other. One drawback resulting from this is that an arbitrary group of users, located separately from each other in the network, is not able to follow a recording in a synchronized manner so that the playback proceeds in the same phase for each user in the group. There are, however, many occasions when this would be desirable.
In known systems allowing synchronized listening and/or watching, the synchronization of the playback is based on a real-time video and/or audio signal sent to each terminal. This is a clear drawback since the real-time signal, such as a high quality video signal, requires a large bandwidth. Moreover, these systems are rigid in the sense that the transmitting party always acts as the master controlling the playback of the recording.
Thus, even though the present systems feature a reverse control channel from the user terminal to the server, several users wishing to follow a recording in a synchronized manner cannot utilize the system flexibly.
One objective of the invention is to obtain a system by means of which the above-mentioned drawbacks can be eliminated and multimedia services can be offered as flexibly as possible in a network where users located separately from each other may have the above-mentioned need.